松软突出煤层水平钻孔反循环气力排屑机理

为了解决顺层钻进瓦斯抽放钻孔成孔难的问题，提出了松软突出煤层瓦斯抽放钻孔钻杆内孔反循环气力排屑新技术，建立煤屑颗粒在钻杆内孔的反循环气力输送数学模型，经仿真求解，分析了输送压力损失及固相速度的变化规律。结果表明，在顺层水平钻孔钻进过程中，煤屑在反循环气力作用下，气流速度在钻杆内孔中上部比较稳定，而在钻杆内孔下部靠近内壁处的气流速度明显下降且小于中心区域；在同一位置输送浓度越大，气流速度也越大；在输送浓度不同的情况下，随着输送气流速度的增加，钻杆内孔的压力损失先降低再增高，在钻杆内孔反循环气力排屑时存在最佳经济速度。

Chip removal mechanism by air reverse circulation during horizontal drilling in soft outburst coal seam

In order to solve the problem of difficult hole-making in gas drainage during bedding drilling process, a new technology of chip removal by air reverse circulation through the drill rod bore during the gas drainage drilling in soft outburst coal seam was put forward. The mathematical model of air reverse circulation conveying on coal cuttings particles in rod bore was established, and the variation laws of conveying pressure loss and solid phase velocity were analyzed by simulation. The results showed that under the effect of air reverse circulation in the process of bedding horizontal drilling, the air velocity in the upper part of drill rod bore is relatively stable, while in the under part of drill rod bore, the air velocity close to the wall decreases significantly and is less than that in the central zone. In the same location the air velocity becomes greater with the increase of conveying concentration. Under different conveying concentration, the pressure loss in the drill rod bore reduces and then increases with the increase of conveying air velocity. There exists a best economic speed in chip removal by air reverse circulation through the drill rod bore.